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Compliance with the new ASME PTC 19.3 TW-2010 standard provides more reliable thermowells. CHANHASSEN, MINN (June 2, 2011) – Emerson Process Management’s Thermowell Calculation Service is now based on the new standard created by American Society of Mechanical Engineers (ASME) that establishes the practical design considerations for thermowell installations.
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Thermowell Calculation Guide In accordance with ASME PTC 19.3 TW-2010 © ABB Group July 26, 2013 | Slide 1
Contents This document will cover the following topics: 1.
Introduction
2.
Using the front page
3.
Frequency ratio
4.
Stress on a thermowell
5.
Completing data entry
6.
Thermowell types
7.
Dimension details
8.
Material reference
9.
Calculation report
10.
Reviewing the results
11.
Troubleshooting
© ABB Group July 26, 2013 | Slide 2
Introduction ASME PTC 19.3 TW-2010 was written to replace ASME PTC 19.3-1974 following some catastrophic failures in non-steam service, these thermowells passed the criteria laid out in 1974.
The 2010 standard includes significant advances in the knowledge of thermowell behaviour. ASME PTC TW-2010 evaluates thermowell suitability new and improved calculations including: §
Various thermowell designs including stepped thermowells
§
Thermowell material properties
§
Detailed process information
§
Review of the acceptable limit for frequency ratio
§
Steady-state, dynamic and pressure stress
© ABB Group July 26, 2013 | Slide 3
Frequency Ratio As the flow passes the thermowell, alternating vortices are created downstream known as shedding vortices. These shedding vortices cause the thermowell to vibrate, if this vortex shedding rate (fs) approaches the natural frequency (fnc) of the thermowell the dynamic bending stress is greatly increased.
X
Flow direction Y
Z
In-line forces
Fluid vortices downstream Transverse forces
Frequency ratio = (vortex shedding rate, fs) / (installed natural frequency, fnc) The ratio limit will be either 0.4 or 0.8 as defined in ASME PTC 19.3 TW-2010 Forces created by the fluid in the Y plane (in-line with flow) are called drag and forces created in the X plane (transverse to flow) are called lift. The vortex shedding rate for the drag and lift must be calculated. The in-line forces (parallel to flow) are approximately 2x the transverse forces. In the 1974 standard in-line forces were not considered © ABB Group July 26, 2013 | Slide 4
Stress on a Thermowell Steady Stress: The Von Mises criteria which uses radial, axial and tangential stresses due to external pressure, it is found on the report as Steady Stress LHSVM. This value must be less than 1.5x the maximum allowable working stress for the thermowell material. (Smax – Sr)2 + (Smax – St)2 + (St – Sr)2 ≤ 1.5S 2 Dynamic stress: The dynamic predicted stress (including drag and lift forces) must not exceed the fatigue stress limit for the thermowell. The fatigue stress limit is based on the material class (A or B)
Pressure stress: The external pressure must not exceed the pressure rating for the tip and shank of the thermowell. This check does not include checks on the connection rating
© ABB Group July 26, 2013 | Slide 5
Using the Front Page Use the Front Page to enter the reference information that will appear on the calculation report The results can be shown in Metric (Pa, MPa) or Imperial units (psi) depending on your customer’s requirements When the data entry is complete, return to the Front Page to initiate printing all items Use the reset button to clear all the information entered Data Entry © ABB Group July 26, 2013 | Slide 6
Completing Data Entry
Fill in the case data including: §
Operating conditions – units can be selected to suit the calculation using the drop downs
§
Thermowell type – see Thermowell Types for sketches
§
Thermowell dimensions – see Dimension Details for where the information can be found. For stepped items bs and Ls should also be filled in, the program will remind you
§
Thermowell design – select the material of the thermowell, if the material you require is not in the list choose User Defined. The mass density of the sensor can be entered here, see Troubleshooting for help
© ABB Group July 26, 2013 | Slide 7
Thermowell Types STR/THREAD
STR/SW
STR/FLG
STR/VAN
STR/WELD
TAP/THREAD
TAP/SW
TAP/FLG
TAP/VAN
TAP/WELD
STEP/THREAD
STEP/SW
STEP/FLG
STEP/VAN
STEP/WELD
KEY: STR = STRAIGHT; TAP = TAPERED; STEP = STEPPED THREAD = THREADED; SW = SOCKET WELD; FLG = FLANGED; © ABB Group July 26, 2013 | Slide 8
VAN = VAN STONE; WELD = WELD-IN
Dimension Details
Note: Ls and bs are only applicable for step-shank thermowells © ABB Group July 26, 2013 | Slide 9
Material Reference The material information comes from ASME B31.1-2007
You will need to enter material information if: §
A material is selected that was not fully covered in ASME B31.1
§
A temperature was selected that was not fully covered in ASME B31.1
§
User Defined material is selected
© ABB Group July 26, 2013 | Slide 10
Calculation Report Project and client details from the Front Page are shown here Input data from the Data Entry sheet is pulled through here including the thermowell type and material details The calculated results are shown in either Metric or Imperial units as selected on the Front Page Thermowell Suitability is the key information The reason for suitability failure can be found in the comments section © ABB Group July 26, 2013 | Slide 11
Reviewing the Results The information shown on the Calculation Report can be found at the far right of the data entry page.
Understanding Comments on the Calculation Report Comment
Meaning
Frequency limit failed
The calculated frequency ratio, r is higher than the acceptable limit, rmax
Steady state failed
The stress on the thermowell due to the external pressure is more than 1.5x the acceptable working stress for the material
Dynamic state failed
The predicted dynamic stress exceeds the fatigue limit set by the material type
Pressure limit failed
The operating pressure is too high for the pressure rating of the thermowell tip or shank
© ABB Group July 26, 2013 | Slide 12
Troubleshooting The calculation may need to be run again following any changes to existing cases. To do this, please press the CALC button.
Default Information It is important to try to gather the correct information to be sure of the accuracy of the calculation. If the information isn’t available, please use the following (taken from ASME PTC 19.3 TW-2010): §
Mass sensor density = 2700 kg/m3
§
Viscosity = 0.001 cP for gases, = 1 cP for liquids
§
Fillet radius, b = 2 mm
If the material information you have is different from the software information, please select User Defined material and enter the information Material Class A = carbon, low alloy, series 4XX, high-alloy steels not in Class B Material Class B = series 3XX, nickel-chromium-iron alloy, nickel-iron-chromium alloy, nickel-copper alloys © ABB Group July 26, 2013 | Slide 13
© ABB Group July 26, 2013 | Slide 14
Thermowell Calculation Guide In accordance with ASME PTC 19.3 TW-2010 © ABB Group July 26, 2013 | Slide 1
Contents This document will cover the following topics: 1.
Introduction
2.
Using the front page
3.
Frequency ratio
4.
Stress on a thermowell
5.
Completing data entry
6.
Thermowell types
7.
Dimension details
8.
Material reference
9.
Calculation report
10.
Reviewing the results
11.
Troubleshooting
© ABB Group July 26, 2013 | Slide 2
Introduction ASME PTC 19.3 TW-2010 was written to replace ASME PTC 19.3-1974 following some catastrophic failures in non-steam service, these thermowells passed the criteria laid out in 1974.
The 2010 standard includes significant advances in the knowledge of thermowell behaviour. ASME PTC TW-2010 evaluates thermowell suitability new and improved calculations including: §
Various thermowell designs including stepped thermowells
§
Thermowell material properties
§
Detailed process information
§
Review of the acceptable limit for frequency ratio
§
Steady-state, dynamic and pressure stress
© ABB Group July 26, 2013 | Slide 3
Frequency Ratio As the flow passes the thermowell, alternating vortices are created downstream known as shedding vortices. These shedding vortices cause the thermowell to vibrate, if this vortex shedding rate (fs) approaches the natural frequency (fnc) of the thermowell the dynamic bending stress is greatly increased.
X
Flow direction Y
Z
In-line forces
Fluid vortices downstream Transverse forces
Frequency ratio = (vortex shedding rate, fs) / (installed natural frequency, fnc) The ratio limit will be either 0.4 or 0.8 as defined in ASME PTC 19.3 TW-2010 Forces created by the fluid in the Y plane (in-line with flow) are called drag and forces created in the X plane (transverse to flow) are called lift. The vortex shedding rate for the drag and lift must be calculated. The in-line forces (parallel to flow) are approximately 2x the transverse forces. In the 1974 standard in-line forces were not considered © ABB Group July 26, 2013 | Slide 4
Stress on a Thermowell Steady Stress: The Von Mises criteria which uses radial, axial and tangential stresses due to external pressure, it is found on the report as Steady Stress LHSVM. This value must be less than 1.5x the maximum allowable working stress for the thermowell material. (Smax – Sr)2 + (Smax – St)2 + (St – Sr)2 ≤ 1.5S 2 Dynamic stress: The dynamic predicted stress (including drag and lift forces) must not exceed the fatigue stress limit for the thermowell. The fatigue stress limit is based on the material class (A or B)
Pressure stress: The external pressure must not exceed the pressure rating for the tip and shank of the thermowell. This check does not include checks on the connection rating
© ABB Group July 26, 2013 | Slide 5
Using the Front Page Use the Front Page to enter the reference information that will appear on the calculation report The results can be shown in Metric (Pa, MPa) or Imperial units (psi) depending on your customer’s requirements When the data entry is complete, return to the Front Page to initiate printing all items Use the reset button to clear all the information entered Data Entry © ABB Group July 26, 2013 | Slide 6
Completing Data Entry
Fill in the case data including: §
Operating conditions – units can be selected to suit the calculation using the drop downs
§
Thermowell type – see Thermowell Types for sketches
§
Thermowell dimensions – see Dimension Details for where the information can be found. For stepped items bs and Ls should also be filled in, the program will remind you
§
Thermowell design – select the material of the thermowell, if the material you require is not in the list choose User Defined. The mass density of the sensor can be entered here, see Troubleshooting for help
© ABB Group July 26, 2013 | Slide 7
Thermowell Types STR/THREAD
STR/SW
STR/FLG
STR/VAN
STR/WELD
TAP/THREAD
TAP/SW
TAP/FLG
TAP/VAN
TAP/WELD
STEP/THREAD
STEP/SW
STEP/FLG
STEP/VAN
STEP/WELD
KEY: STR = STRAIGHT; TAP = TAPERED; STEP = STEPPED THREAD = THREADED; SW = SOCKET WELD; FLG = FLANGED; © ABB Group July 26, 2013 | Slide 8
VAN = VAN STONE; WELD = WELD-IN
Dimension Details
Note: Ls and bs are only applicable for step-shank thermowells © ABB Group July 26, 2013 | Slide 9
Material Reference The material information comes from ASME B31.1-2007
You will need to enter material information if: §
A material is selected that was not fully covered in ASME B31.1
§
A temperature was selected that was not fully covered in ASME B31.1
§
User Defined material is selected
© ABB Group July 26, 2013 | Slide 10
Calculation Report Project and client details from the Front Page are shown here Input data from the Data Entry sheet is pulled through here including the thermowell type and material details The calculated results are shown in either Metric or Imperial units as selected on the Front Page Thermowell Suitability is the key information The reason for suitability failure can be found in the comments section © ABB Group July 26, 2013 | Slide 11
Reviewing the Results The information shown on the Calculation Report can be found at the far right of the data entry page.
Understanding Comments on the Calculation Report Comment
Meaning
Frequency limit failed
The calculated frequency ratio, r is higher than the acceptable limit, rmax
Steady state failed
The stress on the thermowell due to the external pressure is more than 1.5x the acceptable working stress for the material
Dynamic state failed
The predicted dynamic stress exceeds the fatigue limit set by the material type
Pressure limit failed
The operating pressure is too high for the pressure rating of the thermowell tip or shank
© ABB Group July 26, 2013 | Slide 12
Troubleshooting The calculation may need to be run again following any changes to existing cases. To do this, please press the CALC button.
Default Information It is important to try to gather the correct information to be sure of the accuracy of the calculation. If the information isn’t available, please use the following (taken from ASME PTC 19.3 TW-2010): §
Mass sensor density = 2700 kg/m3
§
Viscosity = 0.001 cP for gases, = 1 cP for liquids
§
Fillet radius, b = 2 mm
If the material information you have is different from the software information, please select User Defined material and enter the information Material Class A = carbon, low alloy, series 4XX, high-alloy steels not in Class B Material Class B = series 3XX, nickel-chromium-iron alloy, nickel-iron-chromium alloy, nickel-copper alloys © ABB Group July 26, 2013 | Slide 13
© ABB Group July 26, 2013 | Slide 14